1. Field of the Invention
The present invention relates to a signal processing apparatus for performing signal processing on an audio signal in accordance with a given purpose, and a method therefor.
2. Description of the Related Art
A so-called noise cancellation system is known that is implemented on a headphone device and used to actively cancel an external noise that comes when a sound of content, such as a tune, is being reproduced via the headphone device. Such noise cancellation systems have been put to practical use. There are broadly two types of systems for such noise cancellation systems: a feedback system and a feedforward system.
For example, Japanese Patent Laid-open No. Hei 3-214892 describes a structure of a noise cancellation system in accordance with the feedback system in which a noise inside a sound tube worn on an ear of a user is picked up by a microphone unit provided close to an earphone unit within the sound tube, a phase-inverted audio signal of the noise is generated, and this audio signal is outputted as sound via the earphone unit, so that the external noise is reduced.
Meanwhile, Japanese Patent Laid-open No. Hei 3-96199 describes a structure of a noise cancellation system in accordance with the feedforward system in which, in essence, a noise is picked up by a microphone attached to the exterior of a headphone device, a characteristic based on a desired transfer function is given to an audio signal of the noise, and a resultant audio signal is outputted via the headphone device.